Gunpowder - Manufacturing Technology

Manufacturing Technology

For the most powerful black powder meal, a wood charcoal is used. The best wood for the purpose is Pacific willow, but others such as alder or buckthorn can be used. In Great Britain between the 15th to 19th centuries charcoal from alder buckthorn was greatly prized for gunpowder manufacture; cottonwood was used by the American Confederate States. The ingredients are reduced in particle size and mixed as intimately as possible. Originally this was with a mortar-and-pestle or a similarly operating stamping-mill, using copper, bronze or other non-sparking materials, until supplanted by the rotating ball mill principle with non-sparking bronze or lead. Historically, a marble or limestone edge runner mill, running on a limestone bed was used in Great Britain; however, by the mid 19th century AD this had changed to either an iron shod stone wheel or a cast iron wheel running on an iron bed. The mix was dampened with alcohol or water during grinding to prevent accidental ignition.

Around the late 14th century AD, European powdermakers first began adding liquid during grinding to improve mixing, reduce dust, and with it the risk of explosion. The powdermakers would then shape the resulting paste of dampened gunpowder, known as mill cake, into corns, or grains, to dry. Not only did corned powder keep better because of its reduced surface area, gunners also found that it was more powerful and easier to load into guns. Before long, powdermakers standardized the process by forcing mill cake through sieves instead of corning powder by hand.

The improvement was based on having a reduced surface area of a higher density composition. At the beginning of the 19th century, density was increased further by static pressing. Shoveling the damp mill cake into a two-foot square box, this was placed beneath a screw press and reduced to 1/2 its volume. "Presscake" had the hardness of slate; the dried slabs were then broken with hammers or with rollers, and the granules sorted with sieves into different grades. In the United States, Irenee du Pont, who had learned the trade from Lavoisier, tumbled the dried grains in rotating barrels to round the edges and increase its durability during shipping and handling.

Another advance was the manufacture of kiln charcoal by distilling wood in heated iron retorts instead of burning it in earthern pits; controlling the temperature influenced the power and consistency of the finished gunpowder. In 1863, in response to high prices for Indian saltpeter, DuPont chemists developed a process using potash or mined potassium chloride to convert plentiful Chilean sodium nitrate to potassium nitrate.

During the 18th century gunpowder factories became increasingly dependent on mechanical energy. Despite mechanization, production difficulties related to humidity control, especially during the pressing, were still present in the late 19th century. A paper from 1885 laments that "Gunpowder is such a nervous and sensitive spirit, that in almost every process of manufacture it changes under our hands as the weather changes." Pressing times to the desired density could vary by factor of three depending on the atmospheric humidity.